Air core poloidal magnetic field system for a toroidal plasma producing device

Abstract

A poloidal magnetics system for a plasma producing device of toroidal configuration is provided that reduces both the total volt-seconds requirement and the magnitude of the field change at the toroidal field coils. The system utilizes an air core transformer wound between the toroidal field (TF) coils and the major axis outside the TF coils. Electric current in the primary windings of this transformer is distributed and the magnetic flux returned by air core windings wrapped outside the toroidal field coils. A shield winding that is closely coupled to the plasma carries a current equal and opposite to the plasma current. This winding provides the shielding function and in addition serves in a fashion similar to a driven conducting shell to provide the equilibrium vertical field for the plasma. The shield winding is in series with a power supply and a decoupling coil located outside the TF coil at the primary winding locations. The present invention requires much less energy than the usual air core transformer and is capable of substantially shielding the toroidal field coils from poloidal field flux.

What is claimed is: 
     
       1. In a toroidal plasma confinement device having poloidal and toroidal magnetic fields for confining a toroidal plasma column with a plasma current induced therein along a circular equilibrium axis in a torus vacuum cavity, said poloidal magnetic field being provided by an air core primary magnetic winding, said device further including a plurality of toroidal field coils encompassing said plasma current for providing said toroidal magnetic field, the improvement comprising a magnetic shield winding positioned between the said toroidal field coils and said plasma current, a magnetic decoupling winding wound adjacent to said air core winding, said shield winding having an equal but opposite number of turns as said decoupling winding, a first power circuit, said primary winding being connected in series with said first power circuit, a second power circuit, said shield winding being connected in series with said decoupling winding and to said second power circuit, sensing means mounted near to said plasma current for sensing the plasma current flux from the vacuum cavity, and a feedback control circuit coupled between said sensing means and said second power circuit to thereby control the current to said series connected shield winding and decoupling winding to thus maintain said total shield winding current equal and opposite to said plasma current, whereby during operation of said device to produce an energetic plasma within said vacuum cavity, said toroidal field coils are substantially shielded from any stray pulsed magnetic fields. 
     
     
       2. The device set forth in claim 1, and further including a set of magnetic trim windings having a net zero ampere-turns, said trim windings being utilized for centering said plasma in said vacuum cavity during operation of said device when such is required. 
     
     
       3. The device set forth in claim 2, wherein said toroidal field coils are superconducting.